In the 1930's, it was found by Langmuir and Blodgett that a fatty acid having 16 to 22 carbon atoms could form a mono-molecular film on the surface of water and the film could be built up on a base material but the application of the built-up films has recently begun to be investigated.
The investigations made heretofore are summaried in Kotai Butsuri (Solid Phisics), (12), 45(1982), Thin Solid Films, 68, No. 1 (180), ibid, 99, Nos. 1, 2, and 3 (1983), G. L. Gains, Insoluble Monolayers at Liquid-Gas Interfaces (Interscience Publishers, New York, 1966), etc., but a Langmuir-Blogett's film (hereinafter, is referred to as LB film) by a conventional straight chain saturated fatty acid has a problem that the film is inferior in heat resistance and mechanical strength and hence it cannot be used for practical purpose as it is.
For overcoming the above problems, polymerizing polymer films formed by using unsaturated fatty acids such as .omega.-tricosenoic acid, .omega.-heptadecenoic acid, .alpha.-octadecylacrylic acid, etc., unsaturated esters of fatty acids such as vinyl stearate, octadecyl acrylate, etc., and diacetylene derivatives have been investigated but these films are yet insufficient in heat resistance as well as are not excellent in electric properties.
It is known that some of polymers having a hydrophilic group, such as polyacids, polyalcohols, ethyl acrylate, polypeptides, etc., have a film-forming property but these polymers have never been investigated as polymers modified, in particular, as materials for LB film, and these polymers cannot be used as excellent LB film materials.
On the other hand, polyimide is known for heat-resistive film but the thickness of a film formed by spin coating is at the best 1,000 .ANG. or more, and usually 1 .mu.m or more, in other words, it is very difficult to form a heat-resistive thin film of less than 1,000 .ANG. having no pin holes by using such a polymer. Also, various photosensitive polyimides have been developed but it is also very difficult to obtain a thin film as described above even by using such polyimides.